1. Field of the Invention
The present invention relates to a light emitting element made of III nitride compound semiconductor, a light emitting device using the light emitting element, and a method for manufacturing the light emitting element.
2. Description of the related art
In the light emitting element made of III nitride compound semiconductor, a so-called flip chip structure is used to obtain a high light extraction efficiency. In this flip chip structure, the back side of a sapphire substrate is directed toward the light emitting direction with the luminous layer structure composed of a multiple quantum well structure on the under side. Thereby, the light emitted from the luminous layer is not intercepted by a non-translucent member such as an electrode.
In order to obtain a higher light extraction efficiency in this flip chip structure, a technique for forming irregularities on the back side of the sapphire substrate was described in patent document 1.
Also, refer to patent document 2 that discloses the techniques associated with the invention.
Patent document 1: JP-A-2003-347601
Patent document 2: JP-A-2003-69075
The incident angle of light on the interface between the back side of the sapphire substrate and the outside world can be varied by providing irregularities on the back side of the sapphire substrate. As a result, though the light is totally reflected on the interface when there are not the irregularities, some of the light has a smaller incident angle than the critical angle due to the irregularities, whereby the quantity of light emerging from the sapphire substrate to the outside world increases. That is, the light extraction efficiency is improved.
However, since there is the interface between the sapphire substrate and the luminous layer structure made of III nitride compound semiconductor and both the substrates have different refractive indexes, some of the light emitted from the luminous layer structure is reflected from the interface between the sapphire substrate and III nitride compound semiconductor layer.
Further, the irregularities on the back side of the sapphire substrate as disclosed in patent document 1 are nonparallel to the reflecting surface of the light emitting element, thereby reducing the quantity of totally reflected light. In other words, the total reflection on the interface between the sapphire substrate and the outside world is not completely eliminated.